The present invention relates to a variable geometry exhaust nozzle for an aircraft turbojet engine, more particularly such a variable geometry exhaust nozzle having a single drive collar controlling the positions of all of the exhaust nozzle flaps.
Variable geometry exhaust nozzles for turbojet engines typically comprise inner and outer flap rings wherein each ring has a plurality of driven flaps and a plurality of interlock flaps circumferentially extending between adjacent driven flaps. The plurality of flaps in the outer ring have a forward edge portion pivotally attached to the turbojet engine structure. The inner flap ring may comprise a plurality of inner forward flaps, again having driven flaps and interlock flaps, with the forward edges of the inner forward flaps pivotally connected to the jet engine structure. The inner flap ring also may comprise a plurality of inner rear flaps, each having a forward edge portion pivotally attached to a rear edge portion of a corresponding inner forward flap. Again, the inner rear flaps may comprise driven flaps circumferentially joined by interlock flaps.
Such known nozzles utilize control systems to vary the angular configurations of the flaps relative to a nozzle centerline to vary the configuration of the inner flap ring between a converging-diverging nozzle configuration necessary for supersonic aircraft operation and a converging--converging configuration for subsonic operations. The positions of the outer flaps also move when the inner flaps change the configuration of the nozzle outlet.
The known types of nozzles may be attached directly to the jet engine exhaust, or may be attached to the rearmost portion of a turbojet engine afterburner.
French Patent No. 2,698,409 discloses a variable geometry exhaust nozzle wherein the driven flaps of the outer flap ring are connected to an actuating collar by a cam device and wherein the inner rear driven flaps are connected by link rods to a cowling structure that is axially displaceable to maneuver the flaps into the desired exhaust nozzle configuration. This design necessitates two separate drive systems having two control circuits. French Patents Nos. 1,225,736 and 1,588,791 also disclose variable geometry exhaust nozzles having three sets of flaps and two separate drive systems. The use of such separate drive systems increases the complexity of the nozzle structure, thereby inherently reducing its reliability, and increasing the weight of the nozzle structure.